Just a note, that your PSU is a dual rail power supply, meaning the 500 watts are split between two power "lines". I'm not sure how to correctly explain it, but basically It's like having two separate less powerful PSUs in one (250w + 250w or 300w + 200w), each delivering power through separate connectors. Maybe your motherboard power connectors and your sata and molex connectors are on one rail and PCI connectors are on the other. Using a 300 watt graphics card on a rail that only has 250 watts will result in your computer shutting down. You can probably look up how the power is split and which connection is connected to which rail in PSU manual.

With a single rail PSU, all the power comes from one source so all the connectors are connected to same source and you could, for example, use a 400w graphics card and use 100w for rest of the system on a 500w PSU. So as long as total system power usage is within PSU limit you shouldn't have to worry about how much power individual components use.

Dual rail power supplies could be more stable and safer than single rail since you have two lanes delivering half the energy, but single rail can support can deliver more power to a single component like a power hungry graphics card.

Sometime ago I used an antec 450w with dual rails and it worked fine with AMD 270x, but it shut off when I ran benchmarking software on AMD 280x because the card under load needed more power than was available on the rail it was connected to. You should have no problems with GTX 950/960 and even a 970 should be fine, but just be aware that your PSU is dual rail.

Hope this helps and doesn't confuse you.